Traditionally TV's ability to reach audiences in large numbers with an audio-visual message left few marketers in doubt as to its effectiveness. Now the promise of quantifiable and meaningful communication with consumers on a one-to-one basis via digital media has moved the goalposts for all media. The metrics applied to advertising effectiveness have multiplied and diversified in response to these changes, and are increasingly applied across channels rather than to each medium individually. 

At the same time, the way people access and consume TV content has changed and continues to do so. Digital TV and streaming via the internet has seen the number of channels balloon and the audience in most markets fragment accordingly. As the largest medium in terms of offline investment, TV's effectiveness is scrutinised and debated more than ever before. Inevitably much of that debate involves the comparative effectiveness of TV and online media as marketers allocate more and more of their budgets to digital media.